The present invention relates to methods for hindering the settling of proppant in a subterranean formation. More particularly, the present invention relates to methods of treating subterranean formations with treatment fluids comprising proppant particulate and/or proppant aggregate gas generated suspension aids.
Subterranean wells (e.g., hydrocarbon producing wells, water producing wells, and injection wells) are often stimulated by hydraulic fracturing treatments. In a typical hydraulic fracturing treatment, a treatment fluid is pumped into a wellbore in a subterranean formation at a rate and pressure above the fracture gradient of the particular subterranean formation so as to create or enhance at least one fracture therein. Particulate solids (e.g., graded sand, bauxite, ceramic, nut hulls, and the like), or “proppant particulates,” are typically suspended in the treatment fluid or a second treatment fluid and deposited into the fractures while maintaining pressure above the fracture gradient. The proppant particulates are generally deposited in the fracture in a concentration sufficient to form a tight pack of proppant particulates, or “proppant pack,” which serves to prevent the fracture from fully closing once the hydraulic pressure is removed. By keeping the fracture from fully closing, the interstitial spaces between individual proppant particulates in the proppant pack form conductive pathways through which produced fluids may flow.
A known alternative hydraulic fracturing treatment involves placing a much reduced volume of proppant in a fracture to create a conductive fracture. In such treatments, individual proppant particulates are formed into proppant aggregates. As used herein, the term “proppant aggregate” refers to a coherent body of any proppant particulates, such that the proppant aggregate does not generally become dispersed into smaller bodies without the application of shear. The proppant aggregates may be placed into the fracture in a more spaced apart fashion than individual proppant particulates, so as to form proppant pillars capable of maintaining sufficient integrity to hold open the fracture once the hydraulic pressure is removed and allow for the flow of produced fluids.
In traditional hydraulic fracturing treatments, the specific gravity of the proppant particulates and proppant aggregates may be high in relation to the treatment fluids in which they are suspended for transport and deposit in a fracture. Therefore, the proppant particulates and aggregates may settle toward the bottommost portion of the fracture. For example, where the bottom of a fracture contains uneven surface, as is often the case, the proppant particulates or aggregates may accumulate only or substantially at the bottommost portion of the uneven surface of the fracture. The settling nature of proppant particulates and aggregates in traditional hydraulic fracturing treatments can result in complete or partial occlusion of the portion of the fracture where no proppant particulates or proppant aggregates have collected when the hydraulic pressure is removed (e.g., at the top of the fracture or a bottom portion of the fracture above a bottommost portion). As such, fracture conductivity and production over the life of a subterranean well may be substantially impaired.
One way to compensate for proppant particulate and proppant aggregate settling is to introduce the proppant particulates or aggregates into the fracture in a viscous gelled fluid. Gelled fluids typically require high concentrations of gelling agents and/or crosslinker, particularly when transporting high concentrations of proppant particulates or aggregates in order to maintain them in suspension. As many gelling and crosslinking agents are used in a variety of fluids within and outside of the oil and gas industry, their demand is increasing while their supply is decreasing. Therefore, the cost of gelling and crosslinking agents is increasing, and consequently, the cost of hydraulic fracturing treatments requiring them is also increasing.
Another method of compensating for the settling nature of proppant particulates and aggregates is the introduction of gas-generating mechanisms that introduce sufficient gas to increase proppant particulate or aggregate buoyancy within the treatment fluid. However, the gas is often generated at unwanted intervals within the subterranean formation (e.g., prior to the proppant particulates or aggregates reaching the fracture). Additionally, gas may be generated partially at unwanted intervals and partially at the desired interval, such that the amount of gas generated at the desired interval is insufficient to increase the buoyancy of the proppant particulates or aggregates to overcome settling forces.
The degree of success of a hydraulic fracturing operation depends, at least in part, upon fracture conductivity after the fracturing operation has ceased and production commenced. Therefore, a method of hindering the settling of proppant particulates and/or proppant aggregates suspended in a treatment fluid in order to prevent partial or complete fracture closure may be of value to one of ordinary skill in the art.